Numerous attempts have been made to reduce lost motion between gripping positions on reversible drive wrenches for socket wrenches and the like tools. The less lost motion, the tighter the location in which such tools can be used.
Two basic types of reversible drive mechanisms have been developed:
the ratchet type, which operates on a pawl-and-rack principle; and PA1 the friction-clutch type, which operates by frictionally engaging rollers between two converging surfaces.
The latter type is the mechanism of the present invention.
Although the ratchet is most widely used, it will not be discussed further here, except to mention that it requires from 10 to 15 degrees between positions of engagement, which limits its use in many situations.
Several modifications have been made of the converging surfaces and roller mechanism. One problem with this type of mechanism is its complexity and the number of parts, making it expensive to manufacture and assemble.
Loomis U.S. Pat. No. 1,136,821 discloses pairs of rollers lodged between the inclined surface of a cam and an internal bearing surface. One or the other of each pair of rollers is wedged between cam and internal bearing surface, depending upon the positioning of the cam, and determining the direction of force to be applied to the socket and its load. It has little specific relationship to the present invention.
Cartwright U.S. Pat. No. 4,669,339 is representative of several mechanisms in which single rollers, constrained to be parallel to the axis of a socket engaging post, are moved into one of two positions where they are frictionally wedged between two converging surfaces to transfer the desired torque from a handle to a socket tool.
Williams U.S. Pat. No. 5,136,901 is by the inventor of the present invention, which is an improvement thereon. The basic difference between the present invention and '901 is that the surface upon which the cylindrical roller moves in the '901 patent is fully planar, whereas in the present invention it is convex or planar only upon the portion of the convex surface closest to the internal bearing surface, reducing the amount of movement required before frictional engagement therebetween.